1. Field of the Invention
The present invention relates to bidimensional electromagnetic emission level monitoring equipment and, more particularly, to bidimensional electromagnetic emission level monitoring equipment of the type measuring the electromagnetic field distribution of RF (Radio Frequency) emissions from electronic or similar equipment in a bidimensional plane.
2. Description of the Background Art
Regulations regarding the level of RF emissions from electronic equipment are prescribed in various countries to prevent RF emissions from disturbing the operations of the other electronic equipment. In the U.S.A., for example, FCC (Federal Communications Commission) Regulations, Part 15, Subpart J prescribes the regulation for 30 megahertz to 1 gigahertz RF emissions. Manufacturers of electronic equipment have to accurately evaluate the level of RF emissions from designed equipment and produce equipment meeting the regulations.
One conventional method available for measuring the level of RF emissions from electronic equipment consists of rotating the equipment under test (EUT) on a turntable, receiving RF emissions from the EUT with an antenna which is fixed or moved monodimensionally, and measuring the received emission levels. Such a method is extensively used to determine whether or not electronic equipment meets the prescribed RF emission level.
The prerequisite for the above-described method is that the antenna be located at a predetermined distance from the EUT so as not to strike against the latter. Especially, when the EUT has a quadrilateral or similar configuration having projections and recesses, the antenna has to be placed a great distance from the EUT. Since the distance between the antenna and the EUT is great as mentioned and since it changes, it is difficult to locate the source of RF emissions accurately. This makes it difficult to evaluate RF emissions of electronic equipment at the design stage.
Another method for measuring RF emissions from electronic equipment is disclosed in U.S. Pat. No. 4,829,238. Bidimensional magnetic emission level monitoring equipment disclosed in this U.S. Patent has antennas (magnetic probes) arranged in a matrix in a bidimensional plane for receiving RF emissions. The equipment has a measuring circuit which sequentially accesses RF emissions from an EUT which are received by the individual antennas, thereby determining bidimensional magnetic emission levels. A display displays the magnetic emission levels produced by the measuring circuit on a bidimensional screen thereof. This kind of monitoring equipment successfully produces accurate location data representative of the source of RF emissions of the EUT. However, such equipment is complicated and expensive due to the number of receiving antennas and does not allow the range for measuring the bidimensional magnetic emission level distribution or the distance between measuring points to be set as desired. Furthermore, an accurate electromagnetic emission level distribution is not achievable unless the great number of antennas have the same sensitivity, resulting in time-consuming adjustment.